Histamine antagonists or antihistamines are drugs that relieve allergy symptoms.<br><br>Histamine is a chemical used to identify and remove substances that trigger an allergic response. Â There are four histamine receptors &#40;designated H<sub>1</sub>, H<sub>2</sub>, H<sub>3</sub>, H<sub>4</sub>&#41;. When histamine activates H<sub>1</sub> receptors, symptoms such as rashes, itching, watery eyes and trouble breathing may begin. <br><br>Antihistamines prevent histamine from stimulating the H<sub>1</sub> receptors located in the eyes, nose and throat to relieve swelling and stop leaking fluid. Â First generation antihistamines were non-selective for H<sub>1</sub> receptors and crossed into the brain resulting in drowsiness. Â Newer antihistamines are more selective, reducing this side effect.

What should I tell my health care provider before I take this medicine?

They need to know if you have any of these conditions:-kidney disease-an unusual or allergic reaction to levocetirizine, cetirizine, hydroxyzine, other medicines, foods, dyes, or preservatives-pregnant or trying to get pregnant-breast-feeding

How should I use this medicine?

Take this medicine by mouth with a glass of water. Take it at night. The tablet may be split in half. Do not chew the tablets. Follow the directions on the prescription label. You can take it with or without food. Do not take more medicine than directed. You may need to take this medicine for several days before your symptoms improve.

Talk to your pediatrician regarding the use of this medicine in children. While this drug may be prescribed for children as young as 6 years old for selected conditions, precautions do apply.

What should I watch for while using this medicine?

Visit your doctor or health care professional for regular checks on your health. Tell your doctor or healthcare professional if your symptoms do not start to get better or if they get worse.

You may get drowsy or dizzy. Do not drive, use machinery, or do anything that needs mental alertness until you know how this medicine affects you. Do not stand or sit up quickly, especially if you are an older patient. This reduces the risk of dizzy or fainting spells. Alcohol may interfere with the effect of this medicine. Avoid alcoholic drinks.

Your mouth may get dry. Chewing sugarless gum or sucking hard candy, and drinking plenty of water may help. Contact your doctor if the problem does not go away or is severe.

What side effects may I notice from receiving this medicine?

Side effects that you should report to your doctor or health care professional as soon as possible:-allergic reactions like skin rash, itching or hives, swelling of the face, lips, or tongue-changes in vision or hearing-fever-trouble passing urine or change in the amount of urine

Side effects that usually do not require medical attention (report to your doctor or health care professional if they continue or are bothersome):-cough-dizziness-drowsiness or tiredness-dry mouth-muscle aches